1. Field of the Invention
The apparatus of the present invention relates to downhole tools. More particularly, the present invention relates to a pipe recovery circulation valve spaced intermittently along a drill string in an open hole for providing circulation around a particular segment of the drill string, when a portion of the drill string is lodged in the hole.
2. General Background
In drilling of oil and gas wells, the first portion of the well drilled into the earth is lined with a continuous column of pipe called "casting". This casing would protect the walls of the borehole from collapsing during the drilling process. However, as the borehole is continued down to deeper depths, the casing is no longer utilized and the drill bit is bored into what is referred to as an "open hole"; that is a hole wherein the walls of the borehole are the substrat around the bit and drill string.
In that event, often times for example in the drilling of deviated hole, where one must turn the angle of the drill bit away from the vertical, the drill string will, as it rotates in the borehole, cut a groove into the wall of the borehole and form a "key seat" which becomes a resituated borehole in the drilling. Often times, this would result in a drill string becoming stuck at that point, and it would be unable to circulate. In the event one should attempt to retrieve the drill string by pulling it out of the hole, the string would either stretch or perhaps in the worse case, break or uncouple, and therefore would have to be fished from the hole if possible.
Therefore, it would be beneficial to provide a means along the drill string which would help to dislodge that particular portion of the string from a key seat or collapsed wall of the borehole, and thus retrieve the string without the loss of expensive pipe or rig time.
Several patents have been obtained in the subject matter of downhole circulation tools of the like, the most pertinent as provided in the prior art statement which is being submitted herewith.